Yes, you can do that. All you need to do is go to "Billing" page and find your order that you wish to upgrade.

If you don't know to which order your IP belongs, type/paste it into the search box at the top left of the dashboard and it will show you.

Now that you know your order, click on the small arrow next to the "View" button and a dropdown will appear where you can find "Upgrade". Click on it and there you can upgrade all of the IPs that belong to this order.